1. Field of the Invention
The present invention relates to a power supply apparatus for a vehicle, and more particularly to a power supply apparatus for a vehicle that employs both a high-voltage power source and a low-voltage power source.
2. Description of the Background Art
Japanese Patent Laying-Open No. 11-185536 discloses a technique related to a remote control cable configured with a power supply line and a signal line for operating a remote-controlled type vehicle for high lift work, wherein the power supply line is coated with a shield material connected to the earth.
According to this technique, when the cable is deteriorated with age or damaged by being trampled down, the power supply line comes into contact with the shield coating the line, which causes a short circuit to make a power supply current flow to the earth. If a current of more than a prescribed amount flows by the short circuit, a fuse will be blown to shut off the current. This can prevent erroneous flow of the current from the power supply line to the signal line that would cause an ON signal.
In recent years, an electric vehicle mounted with a high capacity battery providing a power supply voltage of some hundred volts and using the electric power stored in this battery to energize a motor for driving, and a hybrid vehicle using both of such a battery and a gasoline engine, have come into practical use.
A relay called a system main relay is arranged between the high capacity battery and a load circuit such as a motor. Upon collision of the vehicle, it is necessary to cause this system main relay to quickly attain an open state, so as to stop supply of power of a high voltage to the power supply line.
As such, when an ECU (Electronic Control Unit) detects a collision, it sets a control signal for controlling the system main relay to an inactive ground potential, to thereby stop the power supply.
Meanwhile, it is often the case that such a vehicle is mounted with a battery for auxiliary machinery of 12 V for driving the ECU, in addition to the high capacity battery.
In the case of a hybrid vehicle, an inverter is provided which generates an alternating current for driving the motor from a direct current supplied from the high capacity battery. This makes it difficult to secure the space in the engine room located in front of the passenger seat.
For such a reason, the high capacity battery and the battery for auxiliary machinery are sometimes positioned in the trunk room located at the rear of the passenger seat. This requires complicated wiring of the control signal line and the power supply line between the engine room and the trunk room.
Upon collision of the vehicle, the vehicle body is often damaged and deformed. In such a case, a conductive member may cut in the control signal line or the power supply line to cause a short circuit. If the member is the one electrically connected to the grounded vehicle body, even if it bites the control signal line, the control signal line would be fixed to the ground potential, preventing conduction of the system main relay.
In contrast, if a conductive member electrically isolated from the grounded vehicle body, such as a bracket, damages the signal line for controlling the system main relay and/or the power supply line from the battery for auxiliary machinery due to deformation of the vehicle body upon collision, it will cause a short circuit and the control signal line for controlling the system main relay may attain a power supply potential. In such a case, the system main relay, having once been set to the open state by control of the ECU, would become conductive again.